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MELSEC-Q
7 FUNCTION
7.2 Constant Scan
(1) What is Constant Scan?
The scan time differs because the processing time differs depending on whether
the instruction, which is used in the sequence program, is executed or not.
Constant scan is a function to execute the sequence program repeatedly while
maintaining the scan time at a constant time.
Because I/O refresh is made prior to execution of the sequence program, use of
the constant scan function helps maintain the I/O refresh interval at a constant
rate even if the sequence program execution time varies.
Scan time when constant scan is not used
END
5ms
Sequence program
0
END 0
END 0
END 0
END processing
6ms
5ms
Scan time when constant scan setting is set to 7 ms
END
5ms
Sequence program
0
END
0
END processing
2ms
Wait time
6ms
END
0
1ms
5ms
END
0
2ms
7ms
7ms
7ms
Scan time when constant scan is set to 10 ms during multiple program execution
8ms
Sequence program C
END processing
2ms
Wait time
10ms
Sequence program B
Sequence program A
9ms
1ms
10ms
Fig. 7.1 Constant scan operation
REMARK
When using a low speed execution type program, the constant scan function setting
or low speed execution type program execution time must be set.
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Содержание QCPU (Q Mode)
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